1. Field of the Invention
The present invention relates generally to the combustion of natural gas in internal combustion engines, and more particularly relates to a device for mixing natural gas and air to form a mixture which is combustible in a conventional internal combustion engine.
2. Description of the Prior Art
Because of escalating prices for petroleum-based fuels such as gasoline for use in transportation, alternate energy sources have been widely sought both for use in transportation and for industrial and domestic use. Of course, in seeking alternate energy sources the natural tendency is first to examine the feasibility of using locally available energy resources. Certain geographical locations find themselves blessed with certain types of energy resources, while deficient in others. For example, the Middle Eastern countries possess what seems to be a surfeit of petroleum, and hence have not felt the strains to develop alternate energy sources. Certain areas such a Canada, Alaska, and the Gulf States possess petroleum resources in varying degrees, and seem to possess abundant quantities of natural gas on a widespread basis. Still other areas have plentiful resources of natural gas and petroleum but are not conveniently located to petroleum refineries for converting crude petroleum to fuel. Because of the difficulty and expense of transporting and converting crude petroleum into fuels such as gasoline, diesel fuel, fuel oil, and the like, there has been great interest recently in utilization of natural gas as a fuel for transportation.
Because of the relative abundance of natural gas in certain locales as compared to petroleum products or the proximity of refineries, there is accordingly an incentive to employ this relatively abundant resource because of the economies involved. Use of natural gas instead of petroleum for transportation in many locations would result in cost savings both in the procurement of the fuel as well as in the transportation, refining, storage, and usage.
The use of compressed natural gas as an automotive fuel has sometimes presented difficulties due to the incompatibility of natural gas with conventional internal combustion engines. The air to fuel mixture ratio has been found to be extremely critical, for example. It has also been observed that the ignition timing for gasoline as a fuel does not work for natural gas due to the different combustion characteristics of natural gas. However, it is known in the art to provide for combustion of natural gas in internal combustion engines in certain limited applications. One known device allows the mixture of natural gas and air for vehicle engines which do not exceed about 300 cubic inches in displacement.
It has been found that engines of greater displacement than about 300 cubic inches frequently do not reliably operate with some types of prior art natural gas and air mixing devices, most likely because many of these devices are constructed for placement in the path of air flow to the engine. Accordingly, these devices sometimes do not permit a sufficient volume of air and natural gas mixture to enter the engine for reliable combustion. Such an approach to burning natural gas is typically a complete conversion to natural gas as a fuel source, and nessarily precludes the burning of gasoline as an alternate fuel with the ability to switch back and forth between natural gas and gasoline as the fuel source.
Other difficulties have been encountered in adapting conventional internal combustion engines to burn natural gas. Emission control devices currently required under government air pollution laws alter the combustion characteristics of the gasoline/air mixture such that the levels of emissions produced during the combustion of gasoline are acceptable as measured by federal standards. The presence of this emission control equipment has been found to alter the combustion characteristics of natural gas and air provided in many conventional natural gas conversion devices, such that the emission control equipment must be removed in order for the engine to operate at all. Removal of pollution control equipment, of course, effects a complete conversion to natural gas and prevents legally switching back to gasoline.
Additionally, many prior art natural gas and air mixing devices actually require physical modification of the vehicle air cleaner and removal of the air filter in order to incorporate the mixing device, which may be larger than the size of the open area inside the conventional vehicle air filter. These modifications also effect a total conversion to natural gas and preclude the convenient switching between natural gas and gasoline, because the air filter must be replaced and the emission control equipment must be either re-installed or made re-operable in order to convert back to gasoline. All of the foregoing considerations lend to increased cost and complexity in order to burn natural gas.
Other prior art devices for allowing the introduction of natural gas for combustion into an vehicle engine require modifications to the carburetor. For example, one known prior art device provides the natural gas supply line directly into a port or opening made in the side of the carburetor. Frequently, adaptation of the carburetor to accept this type of prior art device requires removal of the carburetor from the engine and installation of appropriate fittings in order to receive the natural gas line. Again, such modifications lend to complexity and cost in conversion of a vehicle to burn the alternate fuel.
Still other prior art types of devices for conversion to natural gas require installation of natural gas injecting equipment in the "horn" or cylindrical air filter extension of the engine air cleaner assembly. Air flow in this type of device is so restricted that the carburetor cannot be used in the manner in which it was originally intended. Thus, these devices also preclude convenient switching back to gasoline as a fuel.
Accordingly, there has long been a need for an efficient and effective device which mixes natural gas and air for combustion in a conventional internal combustion engine without requiring complex and costly alterations to the engine.
There has also been a need for a device which not only allows the efficient combustion of natural gas in the engine, but also allows the rapid and convenient switching between natural gas and gasoline as fuel sources so that advantage may be taken of whatever fuel source is available.